Description (adapted from the Abstract): This Principal Investigator proposes to study the third variable (V3) region of gp120 to identify determinants which may influence vertical transmission of HIV-1 from a mother to her infant. The pattern of glycosylation of the V3 region of HIV-1 variants may be particularly important in this setting and special attention will be directed to this. The proposed studies will test the hypothesis that the genotype and glycosylation pattern in the V3 region of gp120 are important determinants of HIV-1 vertical transmission. The specific aims are to: (1) Clone and sequence V3 region cDNAs from RNA of HIV-1 variants in Ugandan mother-infant pairs that were participants in NIH/WHO studies of pediatric HIV-1 vertical transmission. By these assays the Investigator will characterize the extent of genetic diversity among HIV-1 variants in pregnant Ugandan women and children, and will determine the genotypic relatedness between the viral populations in these persons. Statistical methods will be used to increase the probability that the viral profiles obtained from DNA sequence analysis accurately reflect the profiles of HIV-1 variants in each mother and infant studied. The PCR amplification will be subdivided into 10 aliquots for each sample and 100 clones will be sequences. (2) Determine the pattern of N-linked glycosylation in the V3 region of the variants in each subject using a novel glycosylation assay. (3) analyze data generated in Specific Aims #1 and #2 to identify genotypic features important in HIV-1 vertical transmission. (4) Use heteroduplex assays to define further the role of V3 region genotype in HIV-1 vertical transmission.